Born-Oppenheimer molecular dynamics (BOMD) using single-reference electronic structure methods, such as density functional theory (DFT), is a powerful simulation tool for investigating reaction mechanisms.  One challenge in these simulations is failure of the self-consistent field (SCF) calculation that solves for the Kohn-Sham wavefunction at each MD time step, a problem that is more likely to occur for intermediate structures along reaction pathways where the occupied and virtual molecular orbitals have a small energy separation.  We developed a new simulation method called the Car-Parrinello monitor (<i>CPMonitor</i>) to make BOMD simulations more robust against SCF convergence failures.  During a normal BOMD simulation, CPMonitor stores a buffer containing the positions, velocities, accelerations and density matrices for a small number of the most recent time steps.  If the BOMD simulation encounters a SCF convergence failure, CPMonitor reverts the simulation time to a stored step in the buffer and starts to propagate a Car-Parrinello molecular dynamics (CPMD) simulation in which the electronic variables are dynamical degrees of freedom and SCF iterations are no longer required.  CPMonitor then periodically checks the CPMD trajectory for SCF convergence and, if possible, reverts the simulation back to the normal BOMD mode.  We demonstrate the feasibility of the CPMonitor approach in "nanoreactor" simulations where extreme conditions are used to discover a large number of reaction pathways.

Car–Parrinello monitor method for circumventing self-consistent field convergence failure in reactive Born–Oppenheimer molecular dynamics

2019 Fall National Meeting

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